Is it a bad idea to "test out" of every skill?
I've started doing this with every skill now, but I don't know whether I should or not. I mainly do it because repeating the whole thing over in the refreshing stage is boring, and losing points because of the timer is bothersome. I use Anki for word and phrase memorisation though, so that probably counteracts any problems caused by testing out... maybe.
Another quick question: Are we supposed to leave time between the lessons and the refreshing stage, or is it okay to just do the whole thing in one go?
If you know the material, and it is boring . . . Test out. Go Anki! Yes, it counteracts any problem. (And there's always Memrise!)
If you have time to do the whole thing in one go, why not? Get it done, learn, master, own the material and move on. Just make sure you have fun in the process.
It's better to practice regularly and often, even if it's not much.
Long sessions are exhausting for the brain and are more likely to make you bored of the language.
As for the skills, it doesn't really matter if you prefer to do a different skill every time or just stick with one until you master it. What matters is what you enjoy the most.
And yes I think it's better to leave some time before doing the "refresh" part, but not too much I usually do the "refresh" the day after I finished the first part.
Go ahead and test out. I did this for the first N levels. Eventually I hit areas where I needed work, and couldn't test out on first or second try, and settled down to doing the lessons.
Fairly often, I end up giving feedback on things I miss, and my answer ends up getting accepted as correct. Looks like they're crowdsourcing the set of correct answers...